CIS 644 Thus Oct 28 1999 misc questions

CIS 644 Thus. Oct. 28, 1999 … misc. questions … thread, Runable … communication patterns W 10 B

Exam 1 … covers: class & scenario models open book … < 1. 5 hours Tues Nov 2. on campus … in class off campus … sent email 4: 30 pm C. T. email or fax it back

administrative: > corrections to GRADES file are being made … will be reposted later. > CIS web server was “killed” this week … temporarily moved … … some scripts may not work CIS 644 local pages should be OK now. > I keep up with “urgent” email … rest may wait for a while (will post patterns lists later)

? ? are GRADES 4 digits SSN number? . . . they are KSU student ID number. ? ? send back off-campus homework … no … just class discussion ? ? post “my answer” … no … posted TA’s answer

? ? “ 1. 5” hours for exam … on-campus. . . up to 90 minutes … off-campus … honor system will draw some diagrams … FAX is OK … “asap” if you want to use Rose or other tool, great … don’t count that as part of exam time.

review questions: "class variables" , "class markers" (page 21) c get. List( ; list) … there are times with class methods are required Coad’s use of class methods for collections is optional … not my preference

my preference: the. Airports LOOP | get. Airport( ; an. Airport) -->| | an. Airport | | get. Info( ) ------------>| ENDLOOP translates: loop { an. Airport = the. Airports. get. Airport( i ); }

? ? is this related to aggregation vs composition ? ? … no … I see A vs C as who owns the items who is responsible for keeping refs UML … what are the items "part of"

? ? c new(passenger; a. Reservation) … converts to Java as: a. Reservation = new Reservation(passenger)

? ? Airports | c remove( an. Airport) -->| could translate as: class Airports { Airport[ ] items; … void remove( integer i) { items[ i ] = null ; } }

? ? * get. Values( ; values) … * indicates a loop … calls to multiple objects from the collection

threads use comments: threads are used in: CIS 625 distributed Processing CIS 725 Computer Networks

I use Solaris threads & Posix threads. I use the ACE framework (thread details are hidden within) … at Motorola

at Sprint: . . . Every application … is multi-threaded. . . created our own thread classes in C++ ( inconsistencies with the standard class) e. g. * credit card validation (C++) … allows concurrent requests * vendor communication (C++) … allows concurrent requests * orders system (Java). . Enterprise Java Beans framework (hidden multi-threads )

. . some Java threads. . . more with multi-tasking in real-time OS (OS-9, i. RMX, Unison, Versa. Dos) using C …these OS's have features such as: mailboxes, signals, shared memory for intertask communication semaphores to control access

we use concurrency. . . in modeling aircraft systems for real-time simulation --------------------------threads (multiple processes) are becoming more common in systems we are developing

? ? was there only one thread in the Video Store? ? … Chap 1 … yes … real… no… need to define the "system" arch. assume: one processor, many agents in PD … should be multiple Agent tasks, each with own UI

continuing into Chaps 4 & 5: Coad: "this is easy" UML: : -( objects: passive vs active: process vs thread ADA: object vs task

Java: Runable interface defines run() but is not per se active object Thread implements Runable and is active object Runable object can be executed "in" (with ? ? ) its own thread. … pass object to Thread(Obj). or, Runable object can make its own thread, as Sensor version p. 194

or. . Thread can execute several different runable objects (…invoke their run() ) … in sequence , of course.

threads can have priorities … but current JVMs do not guarentee exact mapping of priorities !! Lea recommends: HI … for system critical threads LO … for background threads Coad mapping … p. 192 : -(

visual representation of active objects: … at Java level, only Thread is really active, … at design (abstract) level, Runable objects can be "active" : -( Coad does not show bold boxes __ __ Ada: /__ / for Task vs [__] for obj.

skim Chap 4, 5 for overview: several different forms for communication passive (polling) timer active (source notifies its listeners) message vs notification: of course, at Java level, notification implemented as message

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